id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
4467	handle a huge list of ForeignKey objects by implementing a CategorizedModelChoiceField	ulda	nobody	"Think of having a model like this:
{{{
PRKAT_CHOICES= (
    ('M','Metrisch'),
    ('MF', 'Metrisch-Fein'),
#   some more here left out for shortness...
)
class Profil(models.Model):
    kategorie=models.CharField('Kategorie',maxlength=4,choices=PRKAT_CHOICES)
    bezeichnung=models.CharField('Bezeichnung',maxlength=30)

}}}
and your database fills up with profile objects in hundreds with different categories.

Now another model is calling this model like
{{{

class Karte(models.Model):
	ba_nr=models.PositiveIntegerField(""BA-Nr"",primary_key=True)
	datum=models.DateField(""Datum"",default=date.today)

	profil=ForeignKey(Profil)
}}}

and in your forms for Karte you get an ugly select filling the screen.

Attached you find a CategorizedModelChoiceField. With this in hand, you subclass ForeignKey to your model specific ProfileKey
{{{
class ProfilKey(models.ForeignKey):
    def formfield(self,**kwargs):
        defaults = {'form_class': CategorizedModelChoiceField, 'queryset': self.rel.to._default_manager.all(), 'category': 'kategorie' , 'callback_link': '/pr/list_of_profiles_for_category/'}
        defaults.update(kwargs)
        return super(ProfilKey, self).formfield(**defaults)

}}}

and change the ForeignKey  definition in your other model to 
{{{
	profil=ProfileKey(Profil)
}}}

Because the whole thing works with a simple kind of ajax, you need a callback function in your urls like this:
{{{
urlpatterns = patterns('myproject.categorizedmodelchoicefield',
    (r'^pr/list_of_profiles_for_category/$','get_choices_for_category',
     { 'queryset': Profil.objects.all(),
       'category_name':'kategorie' } ),
)
}}}

and voilais: in your forms for Karte you get two selects for category and the actual choice value which updates according to the users selection.

you may also use the formfield_callback but why not using the objects if they are handy...

making it work you need:
  * CategorizedModelChoiceField.py attached
  * JsonResponse from djangosnipplets.org
  * http.Request form openjsan.org loaded somewhere in your base templates

I think something like this should be included as example extension to newforms and to using django/json/ajax. therefore i didn't post ant djangosnipplets.

the javascript code maybe looks ugly, but this is because it was the first time i did javascript.
"	New feature	closed	Forms	dev	Normal	wontfix	ForeignKey ModelChoiceField	ulf.dambacher@…	Someday/Maybe	0	0	0	1	0	0